Submission #1095357

#	Time	Username	Problem	Language	Result	Execution time	Memory
1095357		kh0i	Mountains (NOI20_mountains)	C++17	100 / 100	140 ms	19460 KiB

Mountains

#include <bits/stdc++.h>
using namespace std;

using ll = long long;
using pii = pair<int, int>;

#define F first
#define S second
#define sz(x) (int)(x).size()
#define all(x) (x).begin(), (x).end()

mt19937_64 rng(chrono::steady_clock::now().time_since_epoch().count());

ll get_rand(ll l, ll r){
    assert(l <= r);
    return uniform_int_distribution<ll>(l, r)(rng);
}

const int N = 3e5 + 3;

struct Fenwick{
    #define gb(x) (x) & -(x)

    int n;
    vector<ll> bit;

    Fenwick(int n) : n(n), bit(n + 2) {}

    void add(int pos, ll x){
        for(; pos <= n; pos += gb(pos))
            bit[pos] += x;
    }

    ll get(int l, int r){
        ll res = 0;
        --l;
        for(; r > 0; r -= gb(r)) res += bit[r];
        for(; l > 0; l -= gb(l)) res -= bit[l];
        return res;
    }
};

int n;
ll a[N], r[N];
vector<ll> xx;

void solve(){
    cin >> n;
    for(int i = 1; i <= n; ++i){
        cin >> a[i];
        xx.push_back(a[i]);
    }
    sort(all(xx));
    xx.resize(unique(all(xx)) - xx.begin());
    for(int i = 1; i <= n; ++i)
        a[i] = lower_bound(all(xx), a[i]) - xx.begin() + 1;

    Fenwick fi(n);

    for(int i = n; i >= 1; --i){
        r[i] = fi.get(1, a[i] - 1);
        fi.add(a[i], 1);
    }

    Fenwick se(n);
    ll res = 0;

    for(int i = 1; i <= n; ++i){
        res += se.get(1, a[i] - 1) * r[i];
        se.add(a[i], 1);
    }

    cout << res;
}

signed main(){
    cin.tie(nullptr)->sync_with_stdio(false);

    #define task "troll"
    if(fopen(task".inp", "r")){
        freopen(task".inp", "r", stdin);
        freopen(task".out", "w", stdout);
    }

    solve();

    return 0;
}

Compilation message (stderr)

Mountains.cpp: In function 'int main()':
Mountains.cpp:81:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   81 |         freopen(task".inp", "r", stdin);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~
Mountains.cpp:82:16: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   82 |         freopen(task".out", "w", stdout);
      |         ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~

• Subtask 1: 2 / 2
• Subtask 2: 4 / 4
• Subtask 3: 9 / 9
• Subtask 4: 36 / 36
• Subtask 5: 28 / 28
• Subtask 6: 9 / 9
• Subtask 7: 12 / 12